I am not sure who your question is addressed to, but I presume it is for me so I'll try to answer.

The most obvious reason for our use of capital letters is because we do. An obvious sounding answer, but punctuation is all about convention. That said, however, they do serve a purpose. As with all parts of punctuation, capitalisation helps the reader.

I'd like to give you an example.
Look at the two sentences below.

The man, who was Zahzziring Zamzzanly, laughed loudly.
The man, who was zahzziring zamzzanly, laughed loudly.

Do you understand the meaning of Zahzziring Zamzzanly?
Do you understand the meaning of zahzziring zamzzanly?
Why?
Capitalisation tells the reader that Zahzziring Zamzzanly must be the man's name while it's abscence in zahzziring zamzzanly precludes the possibility that it might be the man's name. (Obviously, these words are made up.)
As you can see capitalisation allows the reader to better understand the text, you could recognise the name even though you'd never seen it before.

The fact that proper nouns (eg. names of places and people) are capitalised is also important for scanning.

"By scanning we mean glancing rapidly through a text either to search for a specific piece of information (eg. a name, or a date) or to get an initial impression of whether the text is suitable for a given purpose (eg. whether a book on gardening deals with a particular plant disease)."
(C. Nuttal: Teaching Reading Skills in a foreign language; pg.49)

The very fact that, with the exception of the first word of the sentence, capitalisation is only used for proper nouns makes it much easier to identify names, for example, of places and people; therefore they can be found faster thus creating a more efficient reader. By this I mean one who can quickly extract the information they need from a long text; one who does not read in detail a lot of unnecessary information.

The other reason is that they help illustrate the beginning of a sentence. Obviously, full stops do this, but the reinforcement helps.

I hope this helps. You could try going to the forums section of Dave's and posting it in the appropriate one there. You'd probably get a better explaination than the one I've supplied.

As for being a "slackers/layabouts/ne'erdowells" because you don't know the answer to a question, you seem to being very hard on yourself, and as for me being a "real" teacher, I'm not exactly sure how one of those would be defined.

Best wishes,
Stephen

PS. Most Chinese teachers will have learnt to translate English rather than to read it. This means that they do not possess much in the way of reading skills. By this I mean things like word attack skills (using the context, the vocabulary and the grammar) to help them work out the meaning of a word; they also have probably not been taught skills like scanning. Therefore, it is not suprising that they would be mute on the the question you asked. The Chinese do not learn to read (at school at least), so they haven't been taught to use things such as capital letters to make them better readers.